Vacuum preloading underground water level test system and test method with liquid differential pressure settlement

Abstract

The vacuum preloading underground water level testing system comprises a water level pipe with a hole, the water level pipe is vertically arranged in a foundation of a vacuum preloading system to be tested, an osmometer A is installed at the bottom end in the water level pipe, an osmometer B is installed at the top end in the water level pipe, and an osmometer C is installed in a sand cushion layer; a first sealed water tank is fixedly mounted at the top end of the water level pipe and internally provided with an osmometer D; a second sealed water tank is arranged in the sand cushion layer, and an osmometer E is arranged in the second sealed water tank; the two sealed water tanks are communicated through a coiled pipe and are filled with water. Calculating the relative positions of the underground water level line and the three osmometers according to the pressures of the three osmometers A, B and C; the vertical distance between the sand cushion and the water level pipe is obtained according to the pressure measured by the D osmometer and the E osmometer, the elevation of the top end of the water level pipe is obtained by combining the elevation provided by the settlement observation device, and then the elevation of the underground water level line is calculated.

Description

Technical Field

[0001] This invention relates to the field of detection technology, and in particular to a vacuum preloading groundwater level testing system and method with liquid pressure differential sedimentation. Background Technology

[0002] Vacuum preloading is a soft soil foundation reinforcement technique, belonging to the drainage consolidation method. Vacuum preloading primarily utilizes the negative pressure created by vacuuming to consolidate the soil and increase its strength. However, despite its widespread application, the reinforcement mechanism of vacuum preloading is not fully understood, with one key focus being the groundwater level in the reinforced area. If the groundwater level drops during reinforcement, the reinforcement mechanism of vacuum preloading should also include the increase in preloading load due to precipitation. Therefore, since the maturation of vacuum preloading technology, accurate testing techniques for the groundwater level in the vacuum preloading reinforced area have been a research hotspot in both engineering and academia.

[0003] Groundwater level testing is generally achieved by burying water level pipes. A crucial aspect of testing groundwater levels during vacuum preloading is ensuring the representativeness of the water level at the test point. Under the negative pressure created by vacuum extraction, a seepage field forms within the reinforced soil. After burying the water level pipe, the seepage field at the test point will inevitably be affected by the pipe, but this influence can be minimized through optimized design. The closer the seepage field at the test point is to the seepage field before the water level pipe is buried, the closer the tested groundwater level is to the actual groundwater level in the vacuum preloading zone.

[0004] Existing vacuum preloading groundwater level testing methods are mainly divided into two categories: The first category is the electrical method, which mainly uses changes in loop resistance to estimate the groundwater level. However, this method is difficult to control in the reinforced area due to the difficulty in controlling the moisture content of the testing environment, which often significantly affects resistance. Furthermore, the soil's conductivity is often high, leading to a significant difference between the actual current loop and the designed loop. Therefore, the testing results of the electrical method are generally not very good. The second category is the water level tube method, which creates a liquid surface within a water level tube and estimates the water level by measuring water pressure using a float, laser, or piezometer. The main drawback of this method is that it significantly alters the seepage field near the testing point. The changes mainly come from two aspects. First, the water level pipe often has a large cavity. The air inside the cavity changes volume when the air pressure changes, thus forming a complex water-air coupling effect and altering the seepage field. Second, some existing methods completely connect the water level pipe to the sand cushion layer, turning the water level pipe into a large drainage board. The negative pressure of the sand cushion layer can be transmitted to the water level pipe with almost no resistance, so the seepage field is obviously very different from that without a buried water level pipe. Another disadvantage of the water level pipe method is that water covering the sealing membrane can easily seep into the water level pipe through the gaps between the water level pipe and the soil, thus affecting the accuracy of the measured water level.

[0005] In addition, existing water level measurement methods often require devices that penetrate the sealing membrane. When penetrating the sealing membrane, appropriate measures and careful operation are required to ensure that no air leakage occurs from the penetration point, which places high demands on the operators. Summary of the Invention

[0006] The purpose of this application is to address the technical deficiencies in the existing technology by providing a vacuum preloading groundwater level testing system and method with liquid pressure differential settlement.

[0007] The technical solution adopted to achieve the purpose of this application is: A vacuum preloading groundwater level testing system with liquid pressure differential settlement includes a perforated water level pipe, which is vertically installed in the foundation of the vacuum preloading system to be tested. The water level pipe is filled with sand. A piezometer A is installed at the bottom of the water level pipe, a piezometer B is installed at the top of the water level pipe, and a piezometer C is installed in the sand cushion layer directly above the piezometer B. A first sealed water tank is fixedly installed at the top of the water level pipe, and a piezometer D is installed inside the first sealed water tank; a second sealed water tank is installed inside the sand cushion layer, and a piezometer E is installed inside the second sealed water tank; the first sealed water tank and the second sealed water tank are connected by a serpentine pipe, and the first sealed water tank, the second sealed water tank and the serpentine pipe are all filled with water; It also includes a settlement monitoring device to determine the real-time elevation of the sand cushion layer.

[0008] In the above technical solution, the water level pipe is arranged at the geometric centroid of four or three adjacent drainage plates of the vacuum preloading system.

[0009] In the above technical solution, the top of the water level pipe is buried below the soil surface, and the burial depth is 0.5-1.0 times the spacing of the drainage boards.

[0010] In the above technical solution, the water level pipe is a continuous perforated water pipe, wrapped with filter cloth to prevent the surrounding soil from entering the pipe.

[0011] In the above technical solution, the length of the water level pipe is preferably 1.0m to 3.0m, and the inner diameter is 3cm to 6cm.

[0012] In the above technical solution, the relative positions of the groundwater level and the three piezometers (piezometer A, piezometer B, and piezometer C) are calculated based on their pressures. The real-time elevation of the sand cushion layer can be determined using the settlement monitoring device. Based on the known elevation of the sand cushion layer, the elevation of the piezometer C buried in the sand cushion layer and the elevation of the second sealed water tank containing the piezometer E are obtained. Based on the pressure measured by piezometers D and E, the vertical distance between the first and second sealed water tanks is obtained through the principle of liquid pressure difference. Then, based on the obtained elevation of the second sealed water tank, the elevation of the first sealed water tank containing piezometer D is obtained. The relative positions of piezometer A, piezometer B, and the first sealed water tank are known. Based on the elevation of the first sealed water tank, the elevations of piezometer A and piezometer B can be obtained. Based on the known elevations of piezometers A, B, and C, and combined with the relative positions of the groundwater level and piezometers A, B, and C, the elevation of the groundwater level can be calculated.

[0013] The installation and testing process of this test system is as follows: (1) After the drainage boards in the area to be reinforced are installed, select test points to serve as the installation locations for this test system; (2) Drill a vertical hole at the test point and bury a water level pipe. The top of the water level pipe is 0.5-1.0 times the spacing of the drainage board from the sand cushion layer. The inside of the water level pipe is filled with sand. A piezometer A is installed at the bottom of the inside of the water level pipe, a piezometer B is installed at the top of the inside of the water level pipe, and a first sealed water tank is installed at the top of the water level pipe. A piezometer D is installed in the first sealed water tank. The first sealed water tank is connected to a second sealed water tank through a serpentine pipe. A piezometer E is installed in the second sealed water tank. Both sealed water tanks and the serpentine pipe are filled with water. (3) After the water level pipe is installed in place, backfill the drill hole, then lay a sand cushion layer, and bury the second sealed water tank in the upper part of the sand cushion layer, and install the piezometer C in the sand cushion layer. (4) Lay a sealing membrane on the sand cushion layer to construct a vacuum preloading system for foundation drainage; then place a settlement observation device on the sealing membrane of the vacuum preloading system; (5) Start the vacuum preloading system to drain the foundation, read the readings of five piezometers at the predetermined monitoring frequency, convert them into pressure values, calculate the real-time elevation of piezometers A, B and C, and obtain the relative position of the groundwater level line with piezometers A, B and C. The elevation of the groundwater level line can then be calculated.

[0014] The beneficial effects of this invention are as follows: (1) The water level pipe is buried in the reinforced soil. The top of the water level pipe and the sand cushion layer are separated by the reinforced soil, which avoids the negative pressure in the sand cushion layer from being directly transmitted to the water level pipe and avoids the interference to the seepage field of the test point caused by the direct connection between the sand cushion layer and the water level pipe, thus obtaining a more accurate groundwater level in the reinforced area. (2) The water level pipe is buried in the reinforced soil to avoid water on the sealing membrane seeping into the water level pipe through the intermittent contact between the water level pipe and the soil, thus avoiding the impact of infiltration on the accuracy of the measured water level. (3) The water level pipe is filled with sand along its length. While ensuring that the water level pipe can effectively transmit hydrostatic pressure, it greatly reduces the air volume inside the water level pipe, avoiding the influence of air expansion and contraction on the water level when the pressure changes. On the other hand, it greatly reduces the volume of the water level pipe, significantly improving the synchronicity of the water levels inside and outside the water level pipe.

[0015] This measurement system does not require penetration of the sealing membrane, reducing the risk of air leakage. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the vacuum preloading groundwater level testing system of the present invention.

[0018] Figure 2 This is a schematic diagram of the arrangement of water level pipes.

[0019] Figure 3 This is a schematic diagram of another arrangement of the water level pipe. Detailed Implementation

[0020] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be further described below with reference to specific embodiments.

[0021] This embodiment provides a vacuum preloading groundwater level testing system with liquid pressure differential settlement. This testing system is applied to a vacuum preloading system to detect the water level elevation within the foundation of the vacuum preloading system. The vacuum preloading system is existing technology, and its basic structure is as follows: vertical drainage boards 3 are arranged in an array in the foundation; a sand cushion layer 4 is laid on top of the foundation, with the top of the drainage boards 3 inside the sand cushion layer 4; a sealing membrane 5 is laid on the sand cushion layer 4; and a horizontal drainage pipe is buried within the sand cushion layer 4. This drainage pipe is connected to an external vacuum drainage device, thereby transferring negative pressure to the sand cushion layer 4, and then from the sand cushion layer 4 through the drainage boards 3 to the foundation, creating negative pressure in the foundation. This causes water vapor in the foundation to rise along the drainage boards 3 into the sand cushion layer 4, and then be discharged outward through the drainage pipe within the sand cushion layer 4, thus reinforcing the foundation.

[0022] See appendix Figure 1The vacuum preloading groundwater level testing system with liquid pressure differential settlement provided in this embodiment includes components such as a perforated water level pipe 1, a piezometer 2, a sealed water tank 7, a serpentine pipe 8, and a settlement plate 6. The water level pipe 1 is vertically installed within the foundation of the vacuum preloading system to be tested. During testing, the water pressure or gas pressure measured by the piezometer 2 is used to calculate the position of the water level line in the water level pipe 1. The relative elevation between the sand cushion layer 4 and the water level pipe 1 is detected using the liquid pressure differential principle. This, combined with the elevation of the settlement plate 6, determines the elevation of the water level pipe 1, thus obtaining the water level elevation. The structure and working principle of this testing system are described in detail below.

[0023] The water level pipe 1 is vertically installed within the foundation of the vacuum preloading system to be tested, and preferably located at the geometric centroid of one or three adjacent drainage plates 3 of the vacuum preloading system (see Appendix). Figure 2 and attached Figure 3 To reduce interference with the seepage field (the geometric centroid is located at the position where the horizontal seepage velocity is zero), the top of the water level pipe 1 is buried below the soil surface at a depth of 0.5-1.0 times the spacing of the drainage boards. Its main function is to prevent the negative pressure in the sand cushion layer 4 of the vacuum preloading system from directly entering the water level pipe, thereby significantly interfering with the seepage field at the test point.

[0024] The water level pipe 1 is a continuous perforated water pipe wrapped with filter cloth to prevent surrounding soil from entering the pipe. The length of the water level pipe 1 is preferably 1.0m to 3.0m, and should be as short as possible while sufficiently covering the possible range of water level changes, so as to reduce the interference of inconsistent pore water pressure dissipation in different soil layers on the water level. The water level pipe should have the smallest possible diameter, preferably with an inner diameter of 3cm to 6cm, while still allowing for proper placement of the piezometer.

[0025] The water level pipe 1 is filled with sand. Sand is chosen over clay because the pores between sand particles can effectively transmit hydrostatic pressure, and the sand should be as dense as possible. The main purpose of filling the water level pipe 1 with sand is as follows: sand can occupy most of the space inside the water level pipe; above the water level, the main function of the sand is to displace as much air as possible from the water level pipe to reduce the impact of air expansion and contraction on the water level; below the water level, the main function of the sand is to reduce the volume of water in the hole so that the water levels inside and outside the water level pipe can be balanced as quickly as possible.

[0026] Piezometer A is installed at the bottom of the water level pipe 1, piezometer B is installed at the top of the water level pipe 1, and piezometer C is installed in the sand cushion layer 4 directly above piezometer B. The relative position of the groundwater level line and the three piezometers can be calculated based on the pressure of the three piezometers A, B and C.

[0027] A first sealed water tank is fixedly installed at the top of the water level pipe 1, and a piezometer D is installed inside the first sealed water tank; a second sealed water tank is installed inside the sand cushion layer 4, and a piezometer E is installed inside the second sealed water tank; the first sealed water tank and the second sealed water tank are connected by a serpentine pipe 8 (during the foundation reinforcement process, the distance between the sand cushion layer 4 and the water level pipe 1 will change, and the serpentine pipe 8 can keep the first sealed water tank and the second sealed water tank connected at all times), and the first sealed water tank, the second sealed water tank and the serpentine pipe 8 are all filled with water.

[0028] Settlement monitoring devices such as a settlement plate 6 or settlement observation nails are installed on the top of the sealing membrane 5 of the vacuum preloading system to obtain the real-time elevation of the sand cushion layer 4 (the real-time elevation of the sand cushion layer 4 can be obtained by observing the settlement plate 6 with a level).

[0029] Based on the known elevation of the sand cushion layer 4, the elevation of the piezometer C buried in the sand cushion layer 4 and the elevation of the second sealed water tank containing the piezometer E can be obtained. Based on the pressure measured by piezometers D and E, the vertical distance between the first and second sealed water tanks can be obtained using the principle of liquid pressure difference. Then, based on the obtained elevation of the second sealed water tank, the elevation of the first sealed water tank containing piezometer D can be obtained. Since the positions of piezometer A, piezometer B, and the first sealed water tank on the water level pipe 1 are fixed, and the relative positions of the three are known, the elevations of piezometer A and piezometer B can be determined based on the elevation of the first sealed water tank.

[0030] In summary, by knowing the real-time elevations of piezometers A, B, and C, and combining this with the relative positions of the groundwater level and the three piezometers, the elevation of the groundwater level can be calculated.

[0031] More specifically, the installation and testing process of this test system is as follows: (1) After the drainage boards in the foundation area to be reinforced are installed, select the geometric centroid of 4 or 3 drainage boards as test points to serve as the installation location of this test system. (2) Drill a vertical hole at the test point and bury the water level pipe 1. The top of the water level pipe is 0.5-1.0 times the spacing of the drainage board from the sand cushion layer. The water level pipe 1 is filled with sand. A piezometer A is installed at the bottom of the water level pipe 1. A piezometer B is installed at the top of the water level pipe 1. A first sealed water tank is installed at the top of the water level pipe 1. A piezometer D is installed in the first sealed water tank. The first sealed water tank is connected to a second sealed water tank through a serpentine pipe 8. A piezometer E is installed in the second sealed water tank. Both sealed water tanks and the serpentine pipe are filled with water. (3) After the water level pipe 1 is installed in place, backfill the drill hole, then lay the sand cushion layer 4, and bury the second sealed water tank on the upper part of the sand cushion layer 4, and install the piezometer C in the sand cushion layer 4. (4) Lay a sealing membrane 5 on the sand cushion layer 4 to construct a vacuum preloading system for foundation drainage; then place a settlement observation device on the sealing membrane 5 of the vacuum preloading system. (5) Start the vacuum preloading system to drain the foundation, read the readings of five piezometers at the predetermined monitoring frequency, convert them into pressure values, calculate the real-time elevation of piezometers A, B and C, and obtain the relative position of the groundwater level line with piezometers A, B and C. The elevation of the groundwater level line can then be calculated.

[0032] Furthermore, the data processing procedure is as follows: (1) Obtain the elevations of three piezometers: Piezometer A, Piezometer B, and Piezometer C. Let the density of water be The elevation of the settling plate is The elevation of the sealed water tank equipped with osmometer D is The elevation of the sealed water tank equipped with osmometer E is The pressure of piezometer D is The pressure of piezometer E is The elevation of piezometer B is The elevation of piezometer C is ;make , , After the system is installed, during the entire vacuum pre-compression reinforcement process, , and It can be considered a constant and can be measured directly upon completion of installation; It can be obtained directly through leveling. , ; , ; Elevation of piezometer A It can be calculated from the relative position of the piezometer B during installation; (2) Obtain the water level elevation: Let the water level elevation be The elevations of piezometers A, B, and C are respectively... , , The pressures are respectively , , Then there should be If the three pressures do not satisfy this relationship, the system fails; if the three pressures satisfy this relationship, the groundwater level elevation is determined as follows.

[0033] 1) If If the water level line is located between piezometer C and piezometer B, then: ; The water level elevation can be calculated. .

[0034] 2) If If the water level line is located between piezometer A and piezometer B, then: ; The water level elevation can be calculated. .

[0035] 3) If If the water level is below the range of the water level pipe, it cannot be measured.

[0036] For ease of explanation, spatial relative terms such as “up,” “down,” “left,” and “right” are used in the embodiments to describe the relationship of one element or feature shown in the figures relative to another element or feature. It should be understood that, in addition to the orientations shown in the figures, spatial terms are intended to include different orientations of the device in use or operation. For example, if the device in the figures is inverted, an element described as being “down” of other elements or features would be positioned “up” of those other elements or features. Therefore, the exemplary term “down” can encompass both up and down orientations. The device may be positioned in other ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0037] Moreover, relational terms such as “first” and “second” are used merely to distinguish one component from another that has the same name, without necessarily requiring or implying any such actual relationship or order between the components.

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A vacuum preloading groundwater level testing system with liquid pressure differential settlement, characterized in that: The system includes a perforated water level pipe, which is vertically installed in the foundation of the vacuum preloading system to be tested. The inside of the water level pipe is filled with sand. Piezometer A is installed at the bottom of the inside of the water level pipe, piezometer B is installed at the top of the inside of the water level pipe, and piezometer C is installed in the sand cushion layer directly above piezometer B. A first sealed water tank is fixedly installed at the top of the water level pipe, and a piezometer D is installed inside the first sealed water tank; a second sealed water tank is installed inside the sand cushion layer, and a piezometer E is installed inside the second sealed water tank; the first sealed water tank and the second sealed water tank are connected by a serpentine pipe, and the first sealed water tank, the second sealed water tank and the serpentine pipe are all filled with water; It also includes a settlement monitoring device to determine the real-time elevation of the sand cushion layer.

2. The vacuum preloading groundwater level testing system with liquid pressure differential settlement according to claim 1, characterized in that: The water level pipes are positioned at the geometric centroid of four or three adjacent drainage plates in the vacuum preloading system.

3. The vacuum preloading groundwater level testing system with liquid pressure differential settlement according to claim 1, characterized in that: The top of the water level pipe is buried below the soil surface, with a burial depth of 0.5-1.0 times the spacing of the drainage boards.

4. The vacuum preloading groundwater level testing system with liquid pressure differential settlement according to claim 1, characterized in that: The water level pipe is a continuous perforated water pipe, wrapped with filter cloth to prevent surrounding soil from entering the pipe.

5. The vacuum preloading groundwater level testing system with liquid pressure differential settlement according to claim 1, characterized in that: The length of the water level pipe is 1.0m to 3.0m, and the inner diameter is 3cm to 6cm.

6. The vacuum preloading groundwater level testing system with liquid pressure differential settlement according to claim 1, characterized in that: The relative positions of the groundwater level and the three piezometers (A, B, and C) can be calculated based on their pressure readings. The real-time elevation of the sand cushion layer can be determined using the settlement monitoring device. Based on the known elevation of the sand cushion layer, the elevation of the piezometer C buried in the sand cushion layer and the elevation of the second sealed water tank containing the piezometer E are obtained. Based on the pressure measured by piezometers D and E, the vertical distance between the first and second sealed water tanks is obtained through the principle of liquid pressure difference. Then, based on the obtained elevation of the second sealed water tank, the elevation of the first sealed water tank containing piezometer D is obtained. The relative positions of piezometer A, piezometer B, and the first sealed water tank are known. Based on the elevation of the first sealed water tank, the elevations of piezometer A and piezometer B can be obtained. Based on the known elevations of piezometers A, B, and C, and combined with the relative positions of the groundwater level and piezometers A, B, and C, the elevation of the groundwater level can be calculated.

7. The vacuum preloading groundwater level testing system with liquid pressure differential settlement according to claim 1, characterized in that: The system installation and testing process is as follows: (1) After the drainage boards in the area to be reinforced are installed, select test points to serve as the installation locations for this test system; (2) Drill a vertical hole at the test point and bury a water level pipe. The top of the water level pipe is 0.5-1.0 times the spacing of the drainage board from the sand cushion layer. The inside of the water level pipe is filled with sand. A piezometer A is installed at the bottom of the inside of the water level pipe, a piezometer B is installed at the top of the inside of the water level pipe, and a first sealed water tank is installed at the top of the water level pipe. A piezometer D is installed in the first sealed water tank. The first sealed water tank is connected to a second sealed water tank through a serpentine pipe. A piezometer E is installed in the second sealed water tank. Both sealed water tanks and the serpentine pipe are filled with water. (3) After the water level pipe is installed in place, backfill the drill hole, then lay a sand cushion layer, and bury the second sealed water tank in the upper part of the sand cushion layer, and install the piezometer C in the sand cushion layer. (4) Lay a sealing membrane on the sand cushion layer to construct a vacuum preloading system for foundation drainage; then place a settlement observation device on the sealing membrane of the vacuum preloading system; (5) Start the vacuum preloading system to drain the foundation, read the readings of five piezometers at the predetermined monitoring frequency, convert them into pressure values, calculate the real-time elevation of piezometers A, B and C, and obtain the relative position of the groundwater level line with piezometers A, B and C. The elevation of the groundwater level line can then be calculated.

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